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Microsoft Word C043492e doc Reference number ISO 6721 2 2008(E) © ISO 2008 INTERNATIONAL STANDARD ISO 6721 2 Second edition 2008 06 01 Plastics — Determination of dynamic mechanical properties — Part[.]

Reference number ISO 6721-2:2008(E)

INTERNATIONAL STANDARD

ISO 6721-2

Second edition 2008-06-01

Plastics — Determination of dynamic mechanical properties —

Part 2:

Torsion-pendulum method

Plastiques — Détermination des propriétés mécaniques dynamiques — Partie 2: Méthode au pendule de torsion

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Published in Switzerland

ISO 6721-2:2008(E)

Foreword iv

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 1

5 Test apparatus 3

6 Test specimens 4

7 Number of specimens 5

8 Conditioning 5

9 Procedure 5

10 Expression of results 6

11 Precision 9

12 Test report 9

Annex A (normative) Influence of longitudinal force, W 10

Annex B (informative) Damping correction factor, Fd 11

Annex C (informative) Dimensional correction factor, Fc 12

Bibliography 14

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies) The work of preparing International Standards is normally carried out through ISO

technical committees Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2

The main task of technical committees is to prepare International Standards Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights ISO shall not be held responsible for identifying any or all such patent rights

ISO 6721-2 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical

properties

This second edition cancels and replaces the first edition (ISO 6721-2:1994), of which it constitutes a minor

revision It also incorporates the Technical Corrigendum ISO 6721-2:1994/Cor.1:1995 Apart from the

inclusion of the Corrigendum (which concerns the last sentence in the first paragraph in Annex C), the main

changes are the updating of the references and the correction of ISO 6721-3 to ISO 6721-1 in Subclause 5.6

ISO 6721 consists of the following parts, under the general title Plastics — Determination of dynamic

mechanical properties:

⎯ Part 1: General principles

⎯ Part 2: Torsion-pendulum method

⎯ Part 3: Flexural vibration — Resonance-curve method

⎯ Part 4: Tensile vibration — Non-resonance method

⎯ Part 5: Flexural vibration — Non-resonance method

⎯ Part 6: Shear vibration — Non-resonance method

⎯ Part 7: Torsional vibration — Non-resonance method

⎯ Part 8: Longitudinal and shear vibration — Wave-propagation method

⎯ Part 9: Tensile vibration — Sonic-pulse propagation method

⎯ Part 10: Complex shear viscosity using a parallel-plate oscillatory rheometer

INTERNATIONAL STANDARD ISO 6721-2:2008(E)

Plastics — Determination of dynamic mechanical properties —

Part 2:

Torsion-pendulum method

1 Scope

This part of ISO 6721 specifies two methods (A and B) for determining the linear dynamic mechanical

properties of plastics, i.e the storage and loss components of the torsional modulus, as a function of

temperature, for small deformations within the frequency range from 0,1 Hz to 10 Hz

The temperature dependence of these properties, measured over a sufficiently broad range of temperatures

(for example from −50 °C to +150 °C for the majority of commercially available plastics), gives information on

the transition regions (for example the glass transition and the melting transition) of the polymer It also

provides information concerning the onset of plastic flow The two methods described are not applicable to

non-symmetrical laminates (see ISO 6721-3, Plastics — Determination of dynamic mechanical properties —

Part 3: Flexural vibration — Resonance-curve method) The methods are not suitable for testing rubbers, for

which the user is referred to ISO 4664-2, Rubber, vulcanized or thermoplastic — Determination of dynamic

properties — Part 2: Torsion pendulum methods at low frequencies

2 Normative references

The following referenced documents are indispensable for the application of this document For dated

references, only the edition cited applies For undated references, the latest edition of the referenced

document (including any amendments) applies

ISO 6721-1:2001, Plastics — Determination of dynamic mechanical properties — Part 1: General principles

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 6721-1:2001, Clause 3, apply

4 Principle

A test specimen of uniform cross-section is gripped by two clamps, one of them fixed and the other connected

to a disc, which acts as an inertial member, by a rod The end of the specimen connected to the disc is excited,

together with the disc, to execute freely decaying torsional oscillations The oscillation mode is that designated

IV in ISO 6721-1:2001, Table 2, and the type of modulus is Gto as defined in ISO 6721-1:2001, Table 3

The inertial member is suspended either from the specimen (method A, see Figure 1) or from a wire

(method B, see Figure 2) In the latter case, the wire is also part of the elastically oscillating system

Key

1 upper (fixed) clamp 4 lower (movable) clamp

2 temperature-controlled chamber 5 rod

Figure 1 — Apparatus for method A

Key

1 counterweight 5 upper (movable) clamp

3 inertial member 7 temperature-controlled chamber

Figure 2 — Apparatus for method B

ISO 6721-2:2008(E)

During a temperature run, the same inertial member can be used throughout the whole run, which results in a

frequency decreasing naturally with increasing temperature, or the inertial member can be replaced at

intervals by a member of different moment of inertia in order to keep the frequency approximately constant

During the test, the frequency and the decaying amplitude are measured From these quantities, the storage

component G′to and loss component G″to of the torsional complex modulus G *

to can be calculated

5 Test apparatus

5.1 Pendulum

Two types of torsion pendulum are specified for use with this part of ISO 6721:

a) the inertial member is suspended from the test specimen and the lower end of the specimen is excited

(method A, Figure 1);

b) the inertial member is suspended from a wire attached to a counterweight and the upper end of the

specimen is excited (method B, Figure 2)

Both types of pendulum consists of an inertial member, two clamps for gripping the specimen (one of which is

connected to the inertial member by a rod) and a temperature-controlled chamber enclosing the specimen and

the clamps For method B, a counterweight and connecting wire are also required

5.2 Inertial member

5.2.1 General

The moment of inertia, I, of the inertial member, which may be made of aluminium, for instance, shall be

selected as a function of the torsional stiffness of the specimen, so that the temperature-dependent natural

frequency of the system lies between approximately 0,1 Hz and 10 Hz

When testing standard specimens (see 6.2), a moment of inertia, I, of about 3 × 10−5 kg⋅m2 is recommended if

the same inertial member is to be used throughout a run

NOTE For certain materials, e.g filled polymers, a value of I of about 5 × 10−5 kg⋅m2 may be necessary

If a constant frequency is desired over a broad temperature range, interchangeable inertial members with

different values of I may be used, thereby permitting the moment of inertia to be varied in steps of less than

20 %, i.e the frequency to be corrected in steps of less than 10 % When testing standard specimens (see

6.2) at a frequency of about 1 Hz, a maximum moment of inertia of about 3 × 10−3 kg⋅m2 is recommended

5.2.2 Method A (see Figure 1)

The total mass of the inertial member, the lower clamp and the connecting rod shall be such that the weight,

W, carried by the specimen is not too high [see Annex A, Equation (A.2)]

5.2.3 Method B (see Figure 2)

The total mass of the inertial member, the upper clamp and the rod must be balanced by a suitable

counterweight, so that the longitudinal force, W, acting on the specimen is minimized [see Annex A,

Equation (A.2)] The wire supporting these parts is part of the elastically oscillating system

5.3 Clamps

The clamps shall be designed to prevent movement of the portion of the specimens gripped within them They

shall be self-aligning in order to ensure that the specimen axis remains aligned with the axis of rotation and

the test specimen remains adequately secured over the whole temperature range without distortion occurring,

thus allowing the free length of the specimen to be accurately determined

The movable clamp shall be of low mass

The moment of inertia of the whole system (consisting of the movable clamp, the inertial member and the

connecting rod) shall be determined experimentally

To prevent heat passing from the specimen out of the temperature-controlled chamber and in the opposite

direction, the rod connecting the movable clamp and the inertial member shall be thermally non-conducting

5.4 Oscillation-inducing device

The oscillation-inducing device shall be capable of applying to the pendulum a torsional impulse such that the

pendulum oscillates initially through an angle of not more than 1,5° in each direction for normal materials, or

not more than 3° in each direction for low-modulus materials (such as elastomers)

5.5 Oscillation-frequency and oscillation-amplitude recording equipment

Optical, electrical or other recording systems may be used provided they have no significant influence on the

oscillating system The entire equipment for measuring frequency and amplitude shall be accurate to ± 1 %

(within the transition region ± 5 %)

5.6 Temperature-controlled chamber

See ISO 6721-1:2001, Subclause 5.3

5.7 Gas supply

See ISO 6721-1:2001, Subclause 5.4

5.8 Temperature-measurement device

See ISO 6721-1:2001, Subclause 5.5

5.9 Devices for measuring test-specimen dimensions

See ISO 6721-1:2001, Subclause 5.6

6 Test specimens

6.1 General

See ISO 6721-1:2001, Clause 6

6.2 Shape and dimensions

Rectangular test specimens having the following dimensions are recommended:

ISO 6721-2:2008(E)

Specimens which are rectangular in cross-section but whose thickness and/or width varies along the main

axis of the specimen by more than 3 % of the mean value shall not be used When comparing different

materials, the dimensions of the specimens shall be identical Specimen dimensions differing from the

preferred ones (50 mm × 10 mm × 1 mm) should be chosen to conserve geometric similarity with the preferred

specimen shape

Alternative specimen shapes may be used (e.g cylindrical or tubular); in such cases, dimensions and

tolerances shall be agreed upon by the interested parties

6.3 Preparation

See ISO 6721-1:2001, Subclause 6.3

7 Number of specimens

See ISO 6721-1:2001, Clause 7

8 Conditioning

See ISO 6721-1:2001, Clause 8

If mechanical conditioning of the specimen is required, the specimen shall be twisted through an angle greater

than 5°, but less than 90° in both directions about the torsional-test axis and returned to its normal position

9 Procedure

9.1 Test atmosphere

See ISO 6721-1:2001, Subclause 9.1

9.2 Measurement of specimen cross-section

See ISO 6721-1:2001, Subclause 9.2

9.3 Mounting the test specimens

Clamp the test specimen between the upper and lower clamps The longitudinal axis of the test specimen

shall coincide with the axis of rotation of the oscillating system Any misalignment of the specimen will cause

lateral oscillations that will interfere with the normal oscillation process

After clamping the test specimen, measure the distance between the clamps (the free length L) to ± 0,5 %

When setting up the oscillating system in the chamber, check to make sure that the test specimen is not

stressed

After assembling the oscillating system complete with test specimen, and checking its alignment, start the

heating or cooling (see 9.4)

9.4 Varying the temperature

See ISO 6721-1:2001, Subclause 9.4

9.5 Performing the test

Start the free oscillations by setting the pendulum (5.1) in motion using the oscillation-inducing device (5.4)

Record the oscillation frequency and the oscillation amplitude as it decays

Check that no amplitude decay is caused either by friction between moving and fixed parts of the apparatus or

non-linear behaviour of the material under test (see ISO 6721-1:2001, Annex B)

If the frequency is kept fixed during a temperature run, ensure that the inertial member is changed as and

when necessary

10 Expression of results

10.1 Symbols and correction factors

appropriate, including the movable clamp and the connecting rod)

For specimens with a rectangular cross-section:

where Fc is the so-called dimensional correction factor

When 0 u h/b u 0,6

When 0,6 u h/b u 1

For specimens with a circular cross-section:

where d is the diameter, in metres, of the specimen